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With the increasing concern regarding diesel engine emissions, including nitrogen oxides (NO X ) and particulate matter (PM), and the rising of energy demand as well, the utilization of alternative fuels in diesel engine has been found to be an attractive solution. Natural gas is a very promising and highly attractive fuel because of its domestic availability, widespread distribution infrastructure, low cost, and clean-burning qualities to be used as a transportation fuel. Natural gas/diesel dual fuel is an operation mode in which natural gas is introduced into the intake air upstream of the manifold and then ignited by the direct injected diesel in the cylinder. The aim of this paper is to identify the potential use of natural gas/diesel dual fuel on diesel engine. In this literature review, the combustion, emission and performance characteristics of natural gas/diesel dual fuel combustion-mode published mainly in scientific journals have been collected and critically analyzed. A wide range of natural gas mass ratio which represents the mass fraction of natural gas in the total fuel and different types of engines were involved. It has been found that dual fuel mode has a lower compression pressure and a longer ignition delay compared with normal diesel mode. The application of dual fuel mode significantly decreases the NO X , carbon dioxide (CO 2 ) and PM emissions. However, the hydrocarbon (HC) and carbon monoxide (CO) emissions may increase by several times or even more than 100 times in comparison to normal diesel combustion. And there appears a trade-off relationship between NO X and HC emissions with dual fuel mode. The engine power is decreased up to 2.1% at dual fuel mode, but the power loss can be reduced or recovered by changing some of the operating parameters. The brake thermal efficiency (BTE) of dual fuel mode is lower at low and intermediate loads, while under high engine load conditions it is similar or a little higher when compared with normal diesel mode, and the maximum increase is about 3%. The COV IMEP seems to be generally higher than normal diesel mode and it decreases with the increasing engine load. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the operating range and combustion characteristics in a methanol fumigated diesel engine. The test engine was a six-cylinder, turbocharged direct injection engine with methanol injected into the intake manifold of each cylinder. The experimental results showed that the viable diesel methanol dual fuel (DMDF) operating range in terms of load and methanol substitution percent (MSP) was achieved over a load range from 6% to 100%. The operating range was restricted by four bounds: partial burning, misfire, roar combustion and knock. The lower bound of the operating range was the partial burn bound, which occurred under very low load conditions with high MSP. As the load increased to medium load, MSP reached its maximum value of about 76%, and the onset of misfire provided the right bound for normal operation. At medium to high load, maximum MSP began to decrease. DMDF combustion with excessive MSP was extremely loud with high pressure rise rate, which defined the roar combustion bound. As it increased to nearly full load, measured pressure traces in-cylinder showed strong acoustic oscillations. The appearance of knock provided the upper bound of the operating range. In general, as the load increased, the characters of the combustion changed from partial burn to misfire to roar combustion and to knocking. The range between these four bounds and the neat diesel combustion bound constituted the viable operating range. Over the viable operating range, DMDF combustion worsened the brake thermal efficiency (BTE) at light load while boosted it at medium and high load. [ABSTRACT FROM AUTHOR]

In order to meet the stringent Diesel-engine emission regulations, an aftertreatment system has become more and more popular in many countries. Specifically, to reduce the NO x emissions, a selective catalytic reduction (SCR) system has been successfully applied to many Diesel-engine applications. In the SCR system, NO x sensors are used to monitor the NO x concentration for the control strategies design and fault diagnosis. However, studies show that current NO x sensors are often cross-sensitive to ammonia. Thus, the reading of NO x sensor located at downstream of the SCR catalyst may not be accurate, due to the existing of ammonia slip in the system. Aiming to address this problem, some observers based on Kalman filtering theory are utilized to estimate the cross-sensitivity factor and the actual NO x concentration. Inspired by the fact that the adaptive unscented Kalman filter (AUKF) has the advantages of sample calculation and the capacity to deal with nonlinear system, the AUKF-based observer is investigated to estimate the factor in this paper. In addition, the process noise and measurement noise are usually unknown and time-varying in actual conditions. The AUKF would be effective to update the process and measurement noise covariance matrices online to adapt the practical SCR system. Simulation results through an experimentally-validated full vehicle simulator cX-Emission prove that the performance of designed observer based on AUKF is excellent. [ABSTRACT FROM AUTHOR]